1. Field of the Invention
The present invention relates to a process for remedying medium polluted by a pollutant, and to an apparatus for the same.
2. Description of the Related Art
A large quantity of environmentally unsafe chemical substances have been produced as a result of recent advances in technology. Environmental pollution by chemical substances is a globally serious problem, since water and air can circulate throughout the world. As examples of well-known pollutants, there may be mentioned halogenated aliphatic hydrocarbons (e.g., dichloroethylene (DCE), trichloroethylene (TCE), tetrachloroethylene (PCE) and dioxin), aromatic compounds (e.g., toluene, xylene and benzene), crude petroleum, gasoline and the like. By way of illustration, dichloroethylene, trichloroethylene, tetrachloroethylene and other halogenated aliphatic hydrocarbons have been employed in large quantities as solvents for cleaning of precision parts or for dry cleaning. It has been established that these substances leak into soil and pollute the soil and underground water. Since these pollutants are highly volatile in general, they are also considered to cause air pollution. In addition, they may seriously affect the biotic kingdom, since it has been recently revealed that such pollutants are carcinogenic and teratogenic. Accordingly, there is a demand to develop, promptly, technologies for remedying polluted media such as soil, air and water.
As one possible solution for the aforementioned problems, the technique to decompose pollutants with the aid of microorganisms has been advanced. As microorganisms having decomposing activities for TCE, there have been reported, for example, the following microorganisms.
Welchia alkenophila sero 5 (ATCC 53570; U.S. Pat. No. 4,877,736), PA1 Welchia alkenophila sero 33 (ATCC 53571; U.S. Pat. No. 4,877,736), PA1 Methylocystis sp. strain M (Agric. Biol. Chem., 53,2903(1989); Biosci. Biotech. Biochem., 56,486(1992); ibid. 56,736(1992)), PA1 Methylosinus trichosprium OB3b (Am. Chem. Soc. Natl. Meet. Dev. Environ. Microbiol., 29,365(1989); Appl. Environ. Microbiol., 55,3155(1989); Appl. Biochem. Biotechnol., 28,877(1991); Japanese Patent Laid-open No. 2-92274; Japanese Patent Laid-open No. 3-292970), PA1 Methylomonas sp. MM2 (Appl. Environ. Microbiol., 57,236(1991)), PA1 Alcaligenes denitrificans subsp. xylosoxidans JE75 (Arch. Microbiol., 154,410(1990)), PA1 Alcaligenes eutrophus JMP134 (Appl. Environ. Microbiol., 56,1179(1990)), PA1 Mycobacterium vaccae JOB5 (J. Gen. Microbiol., 82,163(1974), Appl. Environ. Microbiol., 55,2960(1989) ATCC 29678), PA1 Pseudomonas putida BH (Journal of the Japan Sewage Works Association, 24,27(1987)), PA1 Pseudomonas sp. strain G4 (Appl. Environ. Microbiol., 52,383(1986); ibid. 53,949(1987); ibid. 54,951(1988), ibid. 56,1279(1990); ibid. 57,1935(1991); U.S. Pat. No. 4,925,802; ATCC 53617; this microorganism was first classified into Pseudomonas cepacia, but reclassified into Pseudomonas sp.), PA1 Pseudomonas mendocina KR-1 (Bio. Technol., 7,282(1989)), PA1 Pseudomonas putida F1 (Appl. Environ. Microbiol., 54,1703(1988), ibid. 54,2578(1988)), PA1 Pseudomonas fluorescens PFL12 (Appl. Environ. Microbiol., 54,2578(1988)), PA1 Pseudomonas putida KWI-9 (Japanese Patent Laid-open No. 6-70753), PA1 Pseudomonas cepacia KK01 (Japanese Patent Laid-open No. 6-227769), PA1 Nitrosomonas europaea (Appl. Environ. Microbiol., 56,1169(1990)), and PA1 Lactobacillus vaginalis sp. nov. (Int. J. Syst. Bacteriol., 39,368(1989), ATCC 49540) and so on. PA1 (a) providing a membrane between a first medium containing a pollutant and a second medium containing a microorganism capable of decomposing the pollutant, the membrane permeable to the pollutant and impermeable to the microorganism; and PA1 (b) transporting the pollutant from the first medium to the second medium through the membrane to permit the microorganism to decompose the pollutant. PA1 (a) providing an apparatus comprising (i) a tubular case having openings at each end thereof for transporting a first medium containing the pollutant and (ii) a tubular member for transporting a second medium containing a microorganism capable of decomposing the pollutant, the tubular member having an outer wall composed of a membrane permeable to the pollutant and impermeable to the microorganism and being spaced in the tubular case to interpose the membrane between the first medium and the second medium; PA1 (e) embedding the apparatus in the soil containing the pollutant; PA1 (c) conducting the pollutant from the soil into the tubular case through one of the openings; and PA1 (d) introducing the second medium containing the microorganism into the tubular member, whereby the pollutant passes through the membrane to be decomposed by the microorganism. PA1 (a) providing a membrane between a first medium containing a pollutant and a second medium containing a microorganism capable of decomposing the pollutant, the membrane permeable to the pollutant and impermeable to the microorganism; and PA1 (b) transporting the pollutant from the first medium through the membrane to the second medium to permit the microorganism to decompose the pollutant, wherein the transporting step is conducted by providing a flow of the first medium in an opposite direction to a flow of the second medium.
A practical example of a technique for decomposing pollutants and hence remedying media with the aid of such a microorganism includes the process of contacting the microorganism with a pollutant.
Decomposition of pollutants in media with the aid of microorganisms is not as yet a completely satisfactory technique. To be more specific, it is hard to decrease, for example, the trichloroethylene concentration in groundwater to below the environmental quality standard (0.03 .mu.g/ml) in Japan in 1997, and even if possible, it takes a relatively long time for such reaction. To further enhance decomposition of a pollutant by a microorganism, techniques are required for improving decomposition efficiency on the pollutant or for shortening the required period of time for the microorganism to decompose the pollutant.
The present inventors have found that since a microorganism is damaged by an intermediate product or the like formed during decomposition of a pollutant, and its decomposition activity for a pollutant decreases with prolonged contacting time with the pollutant, such a microorganism requires a longer reaction time to decompose the pollutant lower to a given concentration. To further efficiently remedy a medium containing a pollutant in a concentration around the environmental quality standard, it is markedly helpful to contact a microorganism having a high decomposing activity for the pollutant.